High power laser imaging systems

ABSTRACT

An imaging system for use with an input light beam having power of 2 kW or greater and a predetermined intensity profile across at least on axis transverse to a propagation axis thereof, includes a mask disposed in relation to the input light beam, the mask configured to direct selected portions of the input light beam, and an optical relay disposed in relation to the mask and configured to reflectively direct the selected portions of the input light beam to a target.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.12/984,085 filed Jan. 4, 2011 now U.S. Pat. No. 8,835,804, which isincorporated here by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Generally, the field of the present invention is high power lasersystems. More particularly, the present invention relates to high powerlaser systems with high accuracy requirements.

2. Background

Advances in semiconductor lasers permit manufacturers to offerincreasingly higher laser powers at a variety of wavelengths for a widevariety of applications. Typical applications of semiconductor lasersinclude materials processing, communications systems, medical devices,lighting, and analytical instrumentation. In many applications, toprovide even higher optical powers, outputs from multiple devices arecombined using combinations of lenses, mirrors, bulk beamsplitters, andfused fiber couplers. In many cases, laser beams produced bysemiconductor lasers are not circular but elliptical, and typically havediffering beam waists based on the elongated shape of the laser emissionarea.

Some applications impose difficult requirements on beam uniformity anddelivery. While considerable effort has been directed to combining laseroutputs to produce uniform beams that are accurately delivered, theavailable systems nevertheless continue to exhibit some significantlimitations. Thus, despite the considerable efforts that have beenexerted for many years, there remains a need for laser systems thatprovide high power and highly accurate optical beams for variousapplications.

SUMMARY OF THE INVENTION

To satisfy the aforementioned need various aspects and features of thepresent invention provide innovations directed to laser imaging systemssuitable for various high power high precision applications. Accordingto one aspect of the present invention, an imaging system for use withan input light beam having power of 2 kW or greater and a predeterminedintensity profile across at least on axis transverse to a propagationaxis thereof, includes a mask disposed in relation to the input lightbeam, the mask configured to direct selected portions of the input lightbeam, and an optical relay disposed in relation to the mask andconfigured to reflectively direct the selected portions of the inputlight beam to a target.

According to another aspect of the present invention, a method ofprocessing materials with an optical beam of 2 kW or greater generatedby one or more laser sources, includes directing an object optical beamgenerated by the one or more laser sources towards a reflective opticalrelay, reflecting the optical beam through the reflective optical relay,and imaging the optical beam at unit magnification at a work surface.

Additional features and advantages of the present invention will beapparent from the following detailed description of preferredembodiments thereof, which proceeds with reference to the accompanyingdrawings, which are not necessarily drawn to scale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a high power imaging system accordingto an aspect of the present invention.

FIG. 2 is a flow-chart diagram showing an exemplary method according toan aspect of the present invention.

FIG. 3 is a combined perspective and cross-sectional view of an imagingsystem according to an aspect of the present invention, incorporatingone embodiment of an optical relay.

FIG. 4 is a cross-sectional view of another embodiment of an opticalrelay in accordance with another aspect of the present invention.

FIG. 5 is a cross-sectional view of still another optical relay inaccordance with another aspect of the present invention.

FIG. 6 is a side view of the optical relay in FIG. 3 or 4 in accordancewith an aspect of the present invention.

FIG. 7 is another side view of the optical relay in FIG. 3 or 4 inaccordance with an aspect of the present invention.

FIG. 8 is a side view of the optical relay in FIG. 5 in accordance withan aspect of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, a block diagram shows basic aspects of anembodiment of an imaging system 10 providing very high power light in avery accurate manner for materials processing and the like in accordancewith the present invention. The imaging system 10 generally includes alight generating system 12 providing an input optical beam 14 at one ormore suitable wavelengths, e.g., less than 2 μm, directed to a patternmask 16, optical relay 18, and target 22. With additional reference toFIG. 2, an exemplary method 11 is shown in flow-chart form. The inputoptical beam 14 provided by the light generating system 12, for example,as shown in block 13, is directed to the pattern mask 16 and the mask 16allows at least some selected portion 20 of the input optical beam 14 tobe transmitted therethrough towards the optical relay 18, for example,as shown in block 15. In some examples the portion 20 of the inputoptical beam 14 that is transmitted is substantially all of the beam 14while in others the portion 20 that is transmitted is less thansubstantially all of the beam 14, such as 2%, 10%, 50%, or otherpercentages of the input beam 14. In preferred examples the power of theinput optical beam 14 is very high, such as 2 kW or more and the beam 14is provided at a focus thereof in a very small well-defined area, suchas a thin rectangle, or line, having dimensions of 250 mm by 1 mm,though other lengths, widths, and aspect ratios are possible. In someexamples the input beam 14 has a power of 5 kW, 10 kW, 15 kW, or even 20kW or greater and the area in which the beam 14 is provided can belarger, with exemplary rectangular dimensions increasing to or exceeding750 mm by 1 mm. In some embodiments the imaging system 10 issufficiently modular that it includes pattern mask 16 and optical relay18 disposed in relation to each other without the presence of target 22and light generating system 12. However, in other embodiments theimaging system 10 includes the pattern mask 16 and optical relay 18together with the light generating system 12 or the target 22 or both.In some embodiments light generated system 12 includes a plurality ofdiode laser modules which are optically coupled to optical fiber. Instill other embodiments the beams are coupled into one or more beamhomogenizers capable of homogenizing and providing the beams as an inputbeam 14 with a predetermined intensity profile.

Optical relay 18 receives the transmitted optical beam 20 andreflectively directs, or relays, the beam 20 with high precision and lowaberration to target 22, for example, as shown in blocks 17 and 19. Insome embodiments, the numerical aperture of the relayed beam is 0.1 orless across a first axis transverse to the direction of propagation, andapproximately 0.01 across a second axis transverse to the direction ofpropagation. Some examples provide beams 20 projected with a fieldcurvature of less than 500 μm while other examples field curvatures of50 μm or less are achieved. In some embodiments the telecentricity ofthe transmitted beam 20 is less than 40 mrad while in other embodimentstelecentricity is less than 4 mrad. One suitable target 22 for thetransmitted beam 20 in imaging system 10 is a laser induced thermalimaging (LITI) target which is configured to receive the beam 20 so thatthermal imaging can occur. A variety of surfaces may be targeted, thoughtypically beams are directed to a LITI donor film comprised of a basefilm, a light to heat conversion layer, and a transfer layer, such as anelectroluminescent layer made of small molecules or light emittingpolymer. Ultra fast heating caused by the selected incidence of laserradiation on the donor film transfers the electroluminescent layer ontoto an adjacent substrate. Such selective material transfer can be usedfor pixel formation in various display technologies, such as organic LEDmanufacture, and is achievable with higher efficiency than othertechniques by using lasers and systems described herein which exhibithigh accuracy and precision. To satisfy such heightened requirements,particularly at higher powers, numerous problems are encountered whichare solved by the many innovative aspects of the present invention.

In reference to FIGS. 1 and 3, the mask 16 is shown disposed in relationto an object plane 24, or focus, of the input light beam 14 propagatingalong a propagation axis 26. The mask 16 includes a thickness that isgenerally thin, typically ranging several microns to a few millimeters,compared to length and width dimensions which define a planar surface 28thereof. While the planar surface 28 is generally preferred to be flat,in some embodiments the surface 28 may have contour that is other thanflat. The positional relationship between the mask 16 and beam 14 isgenerally defined such that propagation axis 26 of beam 14 isperpendicular to the surface 28 of the mask 16. In some embodiments, themask 16 may be arranged at an angle α with respect to theperpendicularly arranged propagation axis 26 such that the propagationaxis 26 is not perpendicular to the mask 16. During operation of thelight generating system 12 the mask 16 is typically fixed such that thetransmitted beam 20 has a constant shape and profile. When the lightgenerating system 12 is not energized the mask 16 may be moved laterallyso that a different patterned portion 30 is provided for an input beam14 so that a different transmitted beam 20 is produced during subsequentoperation. The mask 16 may also be adjusted rotationally and verticallyfor optimal performance, during or prior to operation.

Mask 16 typically includes one or more patterned portions 30 thattransmit at the wavelength of the beam 14 so that portions of beam 14may propagate past mask 16. By way of example, the patterned portions 30can include holes or perforations in the mask 16 or areas upon which noreflective coating is applied. Accordingly, in some embodimentsnon-patterned areas 32 can include regions where reflective coating isapplied. Thus, as input beam 14 is incident upon the surface 28, atransmitted beam 20 is formed where portions of input beam 14 areallowed to propagate through patterned portions 30 while other portionsof the beam 14 are reflected or otherwise not allowed to propagatethrough the mask 16. A beam dump 23 may be disposed in relation to themask 16 such that reflected light 21 at the mask 16, i.e., thenon-transmitted portions of the beam 14, may be optically coupled to thedump 23. The angle α that can be defined between a perpendicularlyarranged propagation axis allows the non-transmitted portions of thebeam 14 to be reflected away from the propagation axis 26 of the beam 14instead of backwards therealong, thereby preventing potential damage toone or more components of the imaging system 10, including components ofthe light generating system 12. In some embodiments, mask 16 is insteada diffractive, reflective, or absorptive mask. However, more generally,mask 16 is configured to filter and provide an input beam 20 through oneor more conventional techniques. Moreover, in some embodiments mask 16can be patterned to account for distortion or aberrations in relay 18,particularly for multi-mirror embodiments such as four-mirrorembodiments.

As was discussed hereinbefore, in some embodiments the input light beam14 is focused to a narrow aspect rectangle, or line. The transmittedportion 20 begins to diverge after propagating past the mask 16 andobject plane 24. To effectively process different materials or targetsbefore beam divergence adversely affects processing, the target 22 wouldneed to be disposed in close relation to the object plane 24. Thisproximity causes various engineering problems that are largely difficultto directly overcome, especially for advanced applications whichtypically have heightened accuracy requirements and require high power.Included among these problems is a very narrow range for a workingdistance between the mask 16 and target 22. The short working distancecan in turn cause other problems, such as difficulties associated withthermal management, potential damage to the mask, tooling design, etc.

In order to overcome the narrow working distance, the transmitted beam20 is directed through optical components that allow the imaging of thebeam 20 at a location separate from the mask 16. Typically, variouslaser systems, including high power laser systems, direct a focused beamthrough a refractive lens system which refocuses the beam at a separatelocation, thereby providing additional working distance. The lens systemmay also provide aberration correction and magnification. However, asbeam requirements increase, the limits of refractive lens systems becomemore apparent. Referring to the general diagram of FIG. 1, byincorporating significant reflective portions into optical relay 18, theheightened requirements of complex laser systems, including but notlimited to high power line generators, can be met. For example, workingdistances of 0.5 m or greater can be achieved in some embodiments. Byincluding reflective aspects, catoptric as well as catadioptric relayscan be used, including Offner and Dyson designs.

Referring back to FIG. 3, the divergent path of the transmitted portion20 of the beam propagating past the mask 16 is shown generally forexemplary rays 34, 36 near opposite lengthwise ends of a laser lineobject 38 at object plane 24. Marginal rays 34B, 34C of ray 34 divergefrom principal ray 34A as the transmitted portion 20 propagates ontowards optical relay 18. The propagation of ray 36 through relay 18 isomitted for clarity. Optical relay 18 is illustrated in FIG. 3 as areflective relay, may be one similar to those disclosed in U.S. Pat. No.3,748,015 to Offner, which is incorporated herein by reference.

In one embodiment, optical relay 18 includes a pair of transmissivewindows 40, 42 defining a respective beam inlet and outlet thereof, apair of reflective turning mirrors 44, 46, a concave mirror 48 having areflective surfaces 50, 52 for respectively receiving the transmittedbeam 20 from and directing the beam 20 towards the respective turningmirrors 44, 46, and a convex mirror 54 having a reflective surface 56and positioned in relation to the concave mirror 48 so that the beamreflected off surface 50 is convergently received and divergentlyreflected towards surface 52. Concave mirror 48 may include reflectivesurfaces, such as surfaces 50, 52, that are separate and spaced apartfrom each other or the surfaces may be formed in one piece. Withadditional reference to FIGS. 6 and 7, in the Offner design therespective concave and convex reflective surfaces are spherical andconcentrically disposed about a common origin, resulting in a generallysuperior image quality over a rotationally symmetric ring field 114 ofthe relay 18, and resulting in unit magnification with automaticcorrection for all primary aberrations. In some embodimentsmagnifications other than unit magnification are produced. For example,a four mirror system may be used to produce four times unitmagnification. The ring field 114 generally shows where the imagingrelay 18 provides a concentric region of focus and reduced aberration.For example, lines 116, 118 of constant aberration are similarlyconcentric and provide general boundaries for the ring field 114. Across-hatched region 120 of superior focus is shown about a central line122 of best focus and aberration.

Ray 34 reflects off second turning mirror 46 and out throughtransmissive window 42 towards a convergent focus forming a laser lineimage 58 at an image plane 60, which is generally coincident with target22. The turning mirrors 44, 46 are positioned in the relay 18 so as toprovide a co-linear projection from object 38 to image 58, typicallyoriented at 45° with respect to the incident beam 20. Previously omittedray 36 is shown convergently propagating towards image plane 60 aftersecond window 42. The optical path distance between the object 38 andthe reflective surface 50 of the concave mirror 48 is nominally twicethe path length from either one of the surfaces 50, 52 to the convexmirror 54. FIG. 7 shows a similar depiction as FIG. 6 except that adifferent transmitted portion 20 of the input light beam 14 is shownincident on the concave mirror 48.

Referring now to the cross-sectional view of FIG. 4, in anotherembodiment, an optical relay 62 includes a pair of transmissive windows64, 66 forming a general inlet and outlet for a light beam entering andexiting the relay 62, a pair of reflective planar turning mirrors 68,70, an aspheric concave mirror 72 having a reflective surfaces 74, 76for respectively receiving the transmitted beam 20 from and directingthe beam 20 towards the respective turning mirrors 68, 70, and a convexmirror 78 positioned in relation to the concave mirror 72 so that thebeam reflected off surface 74 is convergently received and divergentlyreflected towards surface 76. Convex mirror 78 includes a refractivefirst surface 80, a reflective second surface 82 and an interior portion84, allowing a beam incident on first surface 80 to refract throughinterior portion 84, reflect at second surface 82, and to propagatethrough interior portion 84 and out first surface 80.

An example ray 86, which includes principal ray 86A and correspondingmarginal rays 86B, 86C propagates through relay 62 from an initialstarting point at the object plane 24. The ray 86 passes through window64, reflects off turning mirror 68, and is directed towards firstaspheric surface 74 of concave mirror 72. Ray 86 reflects off surface 74and is directed towards convex mirror 78 where it refracts through firstsurface 80 of convex mirror 78 and propagates through the interiorregion 84 thereof before reflecting off second surface 82 back towardsfirst surface 80 and out divergently towards second surface 76 ofaspheric concave mirror 72. Ray 86 reflects off second surface 76 andconvergently propagates towards second turning mirror 70 which causesthe ray 86 to reflect and continue convergently propagate through secondtransmissive window 66 towards image plane 60. The turning mirrors 68,70 are positioned in the relay 62 so as to provide a co-linearprojection from object plane 24 to image plane 60. In some embodimentsthe projection is other than co-linear. The addition of the refractivefirst surface 80 to convex mirror 78 provides correction for opticalaberrations, including astigmatism. The aspheric aspect of the surfaces74, 76 of the concave mirror further improves image quality. Theorientation of the turning mirrors 68, 70 can vary from 45° orientationwith respect to the incident beam 20 in order to maintain theaforementioned co-linearity as well as telecentricity of the image andobject. In some embodiments the path length between the object 38 andreflective surface 74 or between surface 76 and image 58, and the pathlength between surface 74 and convex mirror 78 is a ratio that is lessthan two, and in some examples significantly less than two.

In another embodiment, referring now to the cross-sectional view of FIG.5, an optical relay 88 includes a pair of transmissive windows 90, 92forming a general inlet and outlet for a light beam entering and exitingthe relay 88, a pair of reflective turning mirrors 94, 96 havingrespective bilaterally symmetric aspheric surfaces 98, 100, a concavemirror 102 having a reflective surfaces 104, 106 for respectivelyreceiving the transmitted beam 20 from and directing the beam 20 towardsthe respective turning mirrors 94, 96, and a convex mirror 108 having areflective surface 110 and positioned in relation to the concave mirror102 so that the beam reflected off surface 104 is convergently receivedand divergently reflected towards surface 106. In some embodiments,concave and convex mirrors 102, 108 are disposed about a common originwhile in others mirrors 102, 108 are not concentrically disposed about acommon origin. An example ray 112, which includes principal ray 112A andcorresponding marginal rays 112B, 112C propagates through relay 88 froman initial starting point at the object plane 24. The ray 112 passthrough window 90, reflects off turning mirror 94, and is directedtowards surface 104 for reflection thereat and towards convex mirror108. Ray 112 reflects at mirror 108 and is directed towards surface 106of concave mirror 102. Ray 112 reflects at surface 106 and isconvergently directed towards second turning mirror 96 and reflects offthe surface thereof and propagates out transmissive window 92convergently towards image plane 60.

The turning mirrors 94, 96 are positioned in the relay 88 so as toprovide a co-linear projection from object plane 24 to image plane 60.In some embodiments the projection is other than co-linear. The turningmirrors 94, 96 can vary from a 45° orientation with respect to theincident beam 20 in order to maintain the aforementioned co-linearity aswell as telecentricity of the image and object. The respective surfaces98, 100 of the turning mirrors 94, 96 can be described by off-axissections of a bilaterally symmetric polynomial such that the surfaces98, 100 are mirror images of each other. There are many suitablesolutions, and corresponding embodiments, for the shape of the surfaces98, 100 which give superior performance. In some embodiments thesurfaces 98, 100 are described by an off-axis section of a rotationallysymmetric asphere, or a conic. In still other embodiments, the surfaces104, 106 of the concave mirror 102 are aspheric. With additionalreference to FIG. 8, a ring field 124 is shown for one opticalconfiguration of relay 88. Ring field 124 includes lines of constantaberration 126, 128 which bound a central line 132 of best focus andaberration. A cross-hatched region 130 of superior focus is shown inrelation to the reflected beam 20. The lines 126, 128, 132 as well asregion 130 are nominally bilaterally symmetric though not rotationallysymmetric. In some embodiments the ring field 124 and region 130 may becharacterized as an oblate, oblong, or elongated annulus or field. Byproviding ring field 124 the transmitted beam 20 can be reflected inbetter overlap therewith, so as to provide better image quality.

It is thought that the present invention and many of the attendantadvantages thereof will be understood from the foregoing description andit will be apparent that various changes may be made in the partsthereof without departing from the spirit and scope of the invention orsacrificing all of its material advantages, the forms hereinbeforedescribed being merely exemplary embodiments thereof.

What is claimed is:
 1. An imaging system comprising: a laser sourcesituated to emit an input light beam and having a predeterminedintensity profile across at least one axis perpendicular to apropagation axis of the input light beam; a mask disposed in relation tothe input light beam so that selected portions of the input light beamare directed through the mask; and an optical relay situated to receivethe selected portions of the input light beam in an elongate bilaterallysymmetric and rotationally asymmetric ring field of reduced aberrationof the optical relay, including at least one reflective asphericsurface, so as to reflect the selected portions of the input light beamto a target.
 2. The imaging system of claim 1, wherein said mask isconfigured to transmit portions of the input light beam therethrough andto reflect non-transmitted portions away from said mask and said opticalrelay.
 3. The imaging system of claim 2 wherein said mask isnon-perpendicular to the propagation axis of the input light beam suchthat the non-transmitted portions of the input laser beam are reflectedat said mask away from the propagation axis of the input light beam. 4.The imaging system of claim 1 wherein the input light beam has a powerof 5 kW or greater.
 5. The imaging system of claim 1 wherein the inputlight beam has a power of 10 kW or greater.
 6. The imaging system ofclaim 1 wherein the input light beam has a power of 15 kW or greater. 7.The imaging system of claim 1 wherein said mask and said optical relayare maintained immovable relative to one another during operation. 8.The imaging system of claim 1 wherein the target is movable with respectto said optical relay.
 9. The imaging system of claim 1, wherein saidoptical relay is situated so as to image the mask at the target withunit magnification.
 10. The imaging system of claim 1, wherein saidoptical relay is situated so as to image the mask at the target withfour times unit magnification.
 11. The imaging system of claim 1,wherein the optical relay is situated to image at least a portion of themask at the target.
 12. The imaging system of claim 1 wherein saidoptical relay is a catadioptric relay.
 13. The imaging system of claim 1wherein said optical relay is a catoptric relay.
 14. The imaging systemof claim 1 wherein said optical relay is an Offner relay.
 15. Theimaging system of claim 1 wherein the target is a laser induced thermalimaging target.
 16. The imaging system of claim 1 wherein the inputlight beam is a line beam with a length of 200 mm or greater.
 17. Theimaging system of claim 1 wherein the input light beam is a line beamwith a length of 750 mm or greater.
 18. A laser imaging systemcomprising: a light generating system for providing a light beam with apredetermined intensity distribution and total power of 2 kW or greatersuch that the light beam at a focus thereof has a narrow aspect ratio;and an off-axis reflective projection relay including a plurality ofmirror elements with at least one having an aspheric surface, the relaydisposed in relation to said light generating system and situated toreceive the light beam in an elongate bilaterally symmetric androtationally asymmetric ring field of reduced aberration of thereflective projection relay and to direct the light beam to an imagelocation.
 19. A laser system capable of emitting a line beam, the lasersystem comprising: a homogenizer optically coupled to an optical beamfor homogenizing the optical beam across at least one transverse axisthereof; and a reflective relay optically coupled to said homogenizerfor receiving the homogenized optical beam and optically imaging thehomogenized optical beam to an imaging surface; wherein the reflectiveoptical relay is a catoptric relay including a concave mirror and aconvex mirror disposed in a concentric relation to one another, and apair of turning mirrors disposed in relation to said concave mirror andsaid convex mirror and optically coupled to said concave mirror, saidturning mirrors having non-planar aspheric surfaces and being mirrorimages of each other.
 20. The laser system of claim 19 wherein theimaged homogenized optical beam is substantially free of opticalaberration.
 21. The laser system of claim 19 wherein said reflectiverelay includes first and second transmissive windows, said first windowadapted to receive a diverging homogenized optical beam, said secondwindow adapted to receive a converging homogenized optical beam.
 22. Thelaser system of claim 19, wherein said reflective relay is an Offnerrelay.
 23. The laser system of claim 19 wherein said reflective relay isa unit-magnification imaging relay.
 24. The laser system of claim 19wherein said reflective relay is self-corrected.
 25. A laser imagingsystem comprising: an optical source that produces an input light beam;an optical mask optically coupled to said optical source, said masksituated to provide a patterned input light beam; and a reflectiveoptical relay optically coupled to said mask, the reflective opticalrelay including a concave outer mirror and a convex inner mirror, theconcave outer mirror being situated to receive the patterned input lightbeam in a first portion of an elongate bilaterally symmetric androtationally asymmetric ring field of reduced aberration and to reflectthe patterned input light beam so as to direct the patterned input lightbeam to the convex inner mirror, the convex inner mirror being situatedto receive the patterned input light beam and to reflect the patternedinput light beam to a second portion of the elongate bilaterallysymmetric and rotationally asymmetric ring field of the concave outermirror.
 26. The laser imaging system of claim 25 wherein the ring fieldis an oblate annulus.
 27. The laser imaging system of claim 25, whereinthe first and second portions of the elongate symmetric ring fieldcorrespond to the elongated portions of the elongate symmetric ringfield and wherein the input light beam is reflected substantially withinthe elongate symmetric ring field first and second portions.
 28. A laserline beam system, comprising: a plurality of diode laser modulesproviding plurality of output beams; a cylindrical lens situated toreceive the plurality of output beams and telecentrically focus theplurality of output beams; a homogenizing light pipe situated to receivethe focused plurality of output beams and configured to homogenize theoutput beams across one or more transverse axes into a singlehomogenized output line beam; and an off-axis reflective relay includinga concave mirror and a convex mirror situated in a non-concentricrelation and having respective centers of curvature lying on a commonsystem axis, the convex mirror having first and second surfaces and aninternal portion, the first surface being anti-reflective so as totransmit light, the second surface being reflective so as to reflectlight received through the internal portion, the off-axis reflectiverelay being situated to receive at least a portion of the homogenizedoutput line beam in a first off-axis portion and configured to reflectthe at least a portion of the homogenized output line beam from a secondoff-axis portion to a target.
 29. The laser system of claim 28, whereinthe concave mirror has an aspheric surface.
 30. A laser inducedthermally imaged surface formed by a method comprising: generating anoptical beam of 2 kW or greater and having an apodized intensityprofile; directing the optical beam to a mask such that a patternedoptical beam is created; and reflectively projecting the patternedoptical beam through an elongate bilaterally symmetric and rotationallyasymmetric ring field of reduced aberration of an optical relay having ato the laser induced thermally imaged surface.
 31. An off-axis imagingrelay comprising: a concave mirror and a convex mirror disposed withrespective centers of curvature situated on a common system axis in anon-concentric relation to one another; said convex mirror having firstand second surfaces and an internal portion, said first surface beinganti-reflective coated so as to substantially transmit light incidentthereon, said second surface being substantially reflective so as toreflect light incident thereon through said internal portion; saidconcave mirror situated to receive light in a first off-axis region froman off-axis object plane and to direct the light to the convex mirror,the concave mirror also situated to receive the light from the convexmirror in a second off-axis region of the concave mirror so as to directthe light to an off-axis image plane.
 32. The imaging relay of claim 31,wherein the concave mirror of said imaging relay has a non-planaraspheric surface.
 33. A method of forming a laser induced thermallyimaged surface, comprising: generating an optical beam having a beampower of 2 kW or greater and having an apodized intensity profile;directing the optical beam to a mask so as to produce a patternedoptical beam; and reflectively projecting the patterned optical beamthrough an optical relay having an elongate bilaterally symmetric androtationally asymmetric ring field of reduced aberration to form thelaser induced thermally imaged surface.
 34. A method of processingmaterials with an optical line beam, the method comprising: directing atleast a portion of the optical line beam generated with one or morelaser sources towards an off-axis reflective optical relay, the off-axisreflective optical relay including concave and convex mirrors havingrespective centers of curvature non-concentrically situated on a commonaxis, the concave mirror situated to receive light in a first off-axisportion and to direct light from a second off-axis portion, the convexmirror having first and second surfaces and an internal portion, thefirst surface being anti-reflective so as to transmit light, said secondsurface being reflective so as to reflect light through the internalportion; reflecting the portion of the optical line beam through thereflective optical relay; and imaging the portion of the optical linebeam at unit magnification at a work surface.
 35. A method of processingmaterials comprising: emitting laser beams from a plurality of laserdiode modules; telecentrically imaging the laser beams into a beamhomogenizer so as to form an homogenized beam having a power of 2 kW orgreater; directing the homogenized beam through a mask so as to form anoutput beam; directing the output beam from an object plane through areflective relay having a pair of non-planar aspheric turning mirrors;and imaging the optical beam at unit magnification to an image plane ata work surface.